Internal combustion engines generally produce engine output torque by performing combustion in the engine cylinders. Specifically, each cylinder of the engine inducts air and fuel and combusts the air-fuel mixture, thereby increasing pressure in the cylinder to generate torque to rotate the engine crankshaft via the pistons. One method to improve engine fuel economy during deceleration is to deactivate fuel injection to all or a selected group of cylinders to thereby reduce combustion torque and increase engine braking.
The above approach can provide engine braking from engine friction and pumping work (due to manifold vacuum). The compression and expansion of air in the cylinders during the compression and expansion stroke results in energy storage and recovery, and thus may not contribute to engine braking. As such, one approach to increase engine braking is referred to as a “Jake Brake”. A Jake Brake opens the exhaust valve at top dead center of compression, thereby reducing or eliminating the energy recovery of the expansion stroke. This, in turn, can increase engine braking significantly since the unrestrained expansion is dissipating energy stored during the compression stroke. An example application is described in U.S. Pat. No. 6,192,857.
However, the inventors herein have recognized several issues with such a system. For example, since the Jake Brake uses compression work to generate braking torque, it must dissipate the stored energy of compression by allowing unrestrained expansion of the compressed gasses. This release of compressed gasses may cause high noise emissions due the rapid release of compressed gas. Furthermore, the maximum amount of pressure generated by compression may be limited due to opening force requirement of the exhaust valve, thereby potentially limiting braking torque available.
In one approach, a method for controlling operation of cylinder with at least an intake and exhaust valve and a piston, the engine in a vehicle, may be used. The method comprises:
maintaining at least one of the intake and exhaust valves in a closed position during a period, and closing the other of the intake and exhaust valves with the piston at a first position from, and then opening the other of the intake and exhaust valves at a second position of the piston closer to bottom center than said first position, during said period.
In this way, it may be possible to reduce flow passing from the intake to the exhaust, while also improving engine braking compared with compression braking systems and reducing noise. In other words, by operating as noted above, it may be possible to generate expansion work braking in the cylinder, in which gasses are expanded in the cylinder and then gasses from a manifold are allowed to expand into the cylinder to dissipate the stored energy. In this way, lower pressure differentials can be achieved compared with compression braking, which may also reduce noise generation.
Note that the above approach can be used alone, or combined with compression braking, if desired. Also note that the opening of the intake valve can be either full or partial opening. Further note that the period can be an expressly defined period, or a variable period, for example.